The present invention relates to an implant material for replacing hard tissue of a living body, and more particularly to novel implant material for replacing a defect or hollow portion of hard tissue, such as bone or dental root, resulting from external injury or surgical removal of bone tumor.
In surgical and orthopedic treatments, prosthesis operations are often required for filling in defects or hollow portions of bone resulting from fracture of bone or surgical removal of bone tumor. Also in the field of dental surgery, similar denture operations are often required for filling in spoilt void portions in maxilla or mandibula resulting from pyorrhea alveolaris. It has been a common practice to resect ilium or other bone tissue from the patient to fill up the defect or hollow portion of bone thereby to promote early remedy of the bone tissue. However, by means of such an operation, normal bone tissue must be picked up from an unspoilt portion which causes additional pain to the patient and in addition the operation is very troublesome. Moreover, when the volume of defect or void in the patient's bone is large, the amount of bone obtainable from his own body is not always sufficient for fully filling in the defect or void. In such a case, it is inevitable to use a substitute for the patient's own bone tissue.
A variety of metal alloys and organic materials have hitherto been used as the substitute for hard tissue in the living body. However, it has been recognized that these materials tend to dissolve or otherwise deteriorate in the environment of living tissue or to be toxic to the living body, and that they cause a so-called foreign body reaction. Ceramic materials are used up to date, since they are excellent in compatibility with living body and are free of the aforementioned difficulties. From ceramic materials, particularly alumina, carbon or tricalcium phosphate or a sintered mass or single crystal of hydroxyapatite, which are superior in compatibility with living body, artificial bones and tooth roots have been developed and have attracted a good deal of public attention.
However, the conventional ceramic implant materials have a common disadvantage in that they are inherently too hard and brittle, and in that they are difficultly machined to have a shape and dimensions adapted to be filled in the void of bone. On the other hand, when alumina is used as the filler, it acts as a stimulant to cause absorption of bone at the vicinity of the implanted filler, since alumina is much harder than the bone tissue. The use of ceramic materials or alumina has not yet been in the stage of practical application, accordingly.
The hard tissues of living body have, in general, a density of about 1.9 g/cm.sup.3, a bending strength of from 300 to 1800 kg/cm.sup.2 and a modulus of bending elasticity of 1.6.times.10.sup.5 kg/cm.sup.2. It is thus desired that the implant material has a bending strength and a modulus of bending elasticity comparable to those of the hard tissues of living body, as set forth above, and a density substantially equivalent to or less than that of the hard tissues of living body, and that it can be easily machined to have a shape and dimensions well adapted to be fitted in a void into which it is implanted. It is further desired that the implant material does not hinder the affinity with the living body but it promotes positively the formation of new bone.